So my mom recently picked up a 2010 Explorer. Pretty nice, very low miles for the year. Around 70k I think. I was checking it out the other day and noticed on cold start (very cold, it was around 5°) there is a fairly loud tick or click noise. Pretty random interval... and seems to go away as soon as it starts to warm up. The thing has a partial warranty for the first month so just wanting to make sure it’s not serious.

So it turns out it's the fan clutch... it's run electrically and unplugging it's plug can stop/cause the noise. Only does it intermittently so if it ends up failing at some point I'll try to remember to update this thread